Officials called the new rules a "seismic shift" in safety, aimed at stemming a string of equine deaths at the track since Christmas.

The home stretch and stands were empty for more than a week at Santa Anita Park in Arcadia, California, where 22 horses have died or been euthanized since Christmas.Damian Dovarganes / AP

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March 14, 2019, 5:43 PM GMT / Updated March 14, 2019, 10:06 PM GMT

By Alex Johnson and David K. Li

LOS ANGELES — Santa Anita Park, the famed California thoroughbred racetrack, announced major reforms on Thursday — including banning the use of drugs on race days and sharply limiting jockeys' use of whips — after a 22nd horse was euthanized following an accident, bringing the number of deaths to 22 since Christmas.

The 3-year-old filly, Princess Lili B, trained by David Bernstein, suffered a catastrophic injury during a workout shortly before 9 a.m. and had to be put down, Santa Anita and state officials said.

In a long statement Thursday, Belinda Stronach, chairman and president of the Stronach Group, said the company would ban the administration of all medications to horses on days they were scheduled to race both at Santa Anita, about 20 miles northeast of downtown Los Angeles, and at Golden Gate Fields, a sister track in Berkeley, California.

Stronach said the new rules would make Santa Anita the first major North American track to comply with the drug policies of the International Federation of Horseracing Authorities, or IFHA.

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Stronach said both tracks would also strictly limit jockeys' use of whips — known in the industry as cushion crops — as a last-ditch corrective safety measure, banning their use to spur horses to run faster.

"While we firmly believe our jockeys have not purposely been mistreating their mounts, it is time to make this change," she said.

The Daily Racing Form, a leading thoroughbred racing industry journal, reported that the only race-day medication allowed in the United States is the diuretic furosemide, which is used to treat bleeding in the lungs, and that use of the drug on race days is the only significant difference between U.S. and IFHA standards.

Stronach owns other prominent tracks in the United States, including Pimlico in Baltimore, the home of the Preakness Stakes, which is one-third of the Triple Crown. Stronach's statement didn't address its other tracks.

Santa Anita officials say they still don't know why so many horses have been breaking down at the park. Industry insiders, veterinarians and animal rights activists have questioned the condition of the dirt track, the treatment of the horses and the pressures of the sport itself.

"We are taking a step forward and saying, quite emphatically, that the current system is broken," Stronach said. "While the cause of the injuries on the racetrack might be varied, they have one thing in common: The industry has yet to do everything that can be done to prevent them. That changes today."

People for the Ethical Treatment of Animals, or PETA — which has called for a criminal investigation at Santa Anita — welcomed the new measures, thanking it in a statement Thursday for "standing up to all the trainers, veterinarians, and owners who have used any means — from the whip to the hypodermic syringe — to force injured or unfit horses to run."

"This is a watershed moment for racing, and PETA urges every track to recognize that the future is now and to follow suit," said PETA, which said it still wanted a criminal investigation "into the trainers whose horses died in the last three months."

HAPPENING NOW: PETA supporters are outside the Los Angeles County District Attorney's office DEMANDING they order an investigation into the trainers and veterinarians following the deaths of TWENTY-TWO horses at the Santa Anita racetrack in just two months 😡 pic.twitter.com/YygGJmWcVW

The rash of deadly spills prompted officials to suspend racing at Santa Anita on March 3, and workouts didn't resume on the main track until Monday. Among the races that were canceled was the $600,000 Santa Anita Handicap on March 9.

While deadly accidents are a constant threat in horse racing, the number of recent deaths stands out. Ten horses died or were euthanized at Santa Anita from Dec. 26, 2017, to March 5, 2018, 11 during the same period in 2016-17 and 16 in 2015-16, according to data from the California Horse Racing Board.

Iconic horses like Azucar, Seabiscuit, Spectacular Bid, Affirmed, American Pharoah and Justify have raced on the oval, which is known as "The Great Race Place," in Arcadia, California.

Alex Johnson reported from Los Angeles. David K. Li reported from New York.